Nowadays, the communication and Information Technology (IT) technologies are developing rapidly. With the emergence of the Internet Protocol (IP) technology that crosses the link-layer transmission media, the Internet applications are popularized rapidly. People are not satisfied with a single voice communication mode any longer, but require brand-new multimedia communication. Therefore, the IP-based mobile communication network, the IP-based fixed communication network, and the convergence of the Internet and the telecom network have become a megatrend in the industry indisputably. In order to meet more and more requirements of IP multimedia applications, the 3rd Generation Partnership Project (3GPP) introduces an IP based Multimedia Subsystem (IMS) in full-IP service network architecture on the basis of the packet bearer network.
The IMS is a subsystem added in the 3GPP R5 stage and overlaid on the existing packet domain in a Wide-band Code Division Multiple Access (WCDMA) network. The IMS uses the packet domain as a bearer channel of its upper-layer control signaling and media, and introduces Session Initiation Protocol (SIP) as a service control protocol. With simplicity and extensibility of the SIP and easy combination of media, the IMS separates the service control from the bearer control, and provides diversified multimedia services.
Main functional entities of the IMS include Call Session Control Function (CSCF) that controls user registration and sessions, Application Server (AS) that provides various service logic control functions, Home Subscriber Server (HSS) that manages subscription data in a centralized way, and Media Gateway Control Function (MGCF)/IP Multimedia Media Gateway Function (IM-MGW) for interworking with the circuit switching network. A user accesses the IMS through the current Proxy Call Session Control Function (P-CSCF). The home-domain Serving Call Session Control Function (S-CSCF) in the registration area of the user is responsible for controlling sessions and the triggering of service, and controlling the service interaction with the AS.
With perfection of the IMS protocol, the IMS based Internet Protocol Television (IPTV) service is developing rapidly. The IMS based IPTV service provides a user with streaming services and the multimedia service that integrates the streaming media with the real-time session service by making full use of the existing mechanisms in the IMS network, for example, registration, authentication, routing, session control and setup, service triggering, charging, and end-to-end Quality of Service (QoS) assurance.
FIG. 1 shows IMS based IPTV service function architecture defined by the Telecommunication and Internet converged Services and Protocols for Advanced Networking (TISPAN), in which an IPTV media server (that is, MF or Media Function) is responsible for controlling and delivering the media streams directed to User Equipment (UE). An IPTV media server is functionally divided into a Media Control Function (MCF) and a Media Delivery Function (MDF). A Service Selection Function (SSF) is responsible for providing the user with available IPTV service information. A Service Control Function (SCF) is responsible for controlling or executing IPTV service logic. The SCF and the MCF are capable of dynamically selecting a media server for an IPTV service requested by the user.
The session creation and media negotiation of the IPTV system are performed through collaboration between the SIP protocol and other protocols such as Realtime Transport Protocol (RTP)/Real-time Transport Control Protocol (RTCP), Session Description Protocol (SDP), Real-Time Streaming Protocol (RTSP), and Domain Name Server (DNS).
The 3GPP has developed specifications of “Transparent End-to-End Packet Switched Streaming Service (PSS)” (that is, PSS Specifications). The PSS Specifications employ a client-server mode. The client (streaming client) communicates with the media server (content server) through GSM EDGE Radio Access Network (GERAN)/UMTS Terrestrial Radio Access Network (UTRAN), 3GPP Core Network, and IP network. In the PSS Specifications, the client creates an RTSP session with the media server through RTSP to negotiate the RTP media delivery channel and receive the media content. The client may send operation commands such as fast-forward and fast-reverse through the RTSP channel to control transmission of media streams.
In the 3GPP specifications, the service control protocol is RTSP rather than the IMS based SIP. Therefore, it is impossible for a SIP-based IMS mobile terminal to join the streaming service effectively. Consequently, the user is unable to enjoy streaming services by making full use of the rich functions provided by the IMS system, for example, uniform user management, QoS control, policy control, charging control, and session setup mechanism. Therefore, the service operation cost of the service provider is increased, and the user experience is deteriorated.